This invention relates to a two-circuit steering system for motor vehicles, especially those systems in which a mechanical linkage connection is provided between the hand steering wheel and the steered parts of the vehicle with an auxiliary fluid power assist associated therewith. The invention is also applicable to those hydrostatic steering systems wherein a linkage connection is omitted and the steering forces are transmitted solely by fluid. The foregoing vehicle steering systems include hand and metering pumps which act in concert with a high pressure pump as a fluid metering arrangement and, in the event of high pressure pump failure, act as hand pumps.
A two-circuit steering system having a high pressure pump is already known. In such a system, steering maneuverability is lost as soon as the high pressure output of the pump is interrupted. In order to cope with this problem, two separate high pressure pumps have been proposed in a system wherein both pumps are driven by the vehicle engine. Whenever the engine fails during travel of the vehicle, drive of the high pressure pump is lost. Consequently, the hand and metering pumps associated with the steering system then act as hand pumps which must be operated solely by muscular power of the vehicle driver. The heavier the vehicle, the more power must, in such case, be expended by the driver for steering purposes. In case of a very heavy vehicle, effective steering is not possible.